Induction of Polygalacturonase fromRhizoctonia solaniby Cotton Seed and Hypocotyl Exudates

Abstract

Endopolygalacturonase (EPG) was first detected in 0.5 M NaCl extracts collected from cotton [Gossypium hirsutum] seedling hypocotyls 18 h after inoculation with R. solani. The units of EPG activity in extracts collected 12, 18, 24, 48 and 72 h after inoculation were 0, 17.5, 36.0, 39.6 and 28.8, respectively. By 18 h after inoculation, infection cushions had formed and by 22-24 h the hypocotyl tissue beneath the cushions was slightly discolored. Neither pectin lyase nor pectate lyase was detected in any of the extracts. The fungus produced extracellular EPG in 0.1% sodium polypectate, in nondialyzed seed exudates and in dialyzed seed exudates. A 24 h after seeding with R. solani, the units of EPG activity in the above preparations were 28, 4 and 256, respectively. The seed exudates (1 ml/4 seeds) were obtained by incubating cotton seeds in water at 22.degree. C for 3 h. The dialyzed and nondialyzed cotton seed exudates contained about 20 .mu.g of galacturonic acid polymers per milliliter. Solutions obtained by exposing cotton hypocotyls to a commercial pectinase solution for 4 h or to 0.05 M HCl for 1 h, induced the fungus to produce 5.6 and 0.4 units, respectively, of EPG activity 24 h after seeding. R. solani produces EPG in response to host exudates.